1. Technical Field
The present invention relates to a label printer that conveys and prints to label paper having labels affixed with a specific interval there between on a continuous liner. The invention relates more particularly to a label paper indexing control method and to a label printer that can reduce the number of labels that are wasted by being positioned downstream in the transportation direction from the printing position when indexing the label paper to position the target printing start position that is preset on the labels to the printing position of the print head.
2. Related Art
When the power is turned on for a label printer that conveys and prints to label paper having labels affixed with a specific interval there between on a continuous liner through a paper transportation path that passes the printing position of the print head, an indexing operation is executed to position the target printing start position preset on the labels to the printing position. Indexing is accomplished by conveying the label paper through the paper transportation path, detecting a reference position such as the leading edge of the labels or index marks on the liner by means of a photo sensor disposed to a detection position on the paper transportation path, and conveying the liner only a predetermined distance from when the reference position (mark) is detected. When indexing ends, printing can proceed based on print commands and print data supplied to the label printer from an external device, for example.
The label printer taught in Japanese Unexamined Patent Appl. Pub. JP-A-2003-312070 detects the reference position for indexing at a detection position that is downstream from the printing position. The label printer taught in Japanese Unexamined Patent Appl. Pub. JP-A-H07-246738 detects the reference position for indexing at a detection position upstream from the printing position.
In order to detect the reference position, the liner must be conveyed passed the detection position and change in the output level of a signal from a photo sensor or other detector must be obtained. Therefore, when indexing is done after the power is turned on, a label with a reference position on the upstream side of the detection position is used as the target label to be indexed (referred to as the “target label” or “indexing target label” below), and the target printing start position of this target label is positioned to the printing position while conveying the liner downstream. After indexing is completed, printing starts from the indexed target label.
When indexing occurs in a label printer in which the detection position is set upstream from the printing position, labels that are downstream from the target label will pass the printing position and be positioned downstream from the printing position. Because printing starts from the target label, labels that are downstream from the target label will not be used for printing and will be needlessly consumed. More particularly, when the print head is an inkjet head, a long distance is provided between the printing position of the inkjet head and the detection position of the photo sensor in order to prevent spray from the ink droplets, for example, discharged from the inkjet head from soiling the photo sensor. As a result, there are plural labels located between the detection position and the printing position, and all of these plural labels will be wasted if the reference position of the target label to be indexed is upstream from the detection position.